Is there any caffeine in decaffeinated coffee?

About 3% of caffeine is normally left in decaf.

A five-ounce cup of coffee will normally contain 75 to 155 milligrams of caffeine. Normally the denser beans grown at high altitudes have a lower caffeine content, as do darker roasted coffees. Arabica usually contain 1-1.5% caffeine by weight. To qualify as decaffeinated they must have 97% of this 1-1.5% removed.

Yes, decaffeinated coffee as well as decaffeinated tea still contains caffeine. So, according to the calculations provided by Jimmy, if you drink ten cups of decaffeinated coffee, you will have consumed the amount of caffeine in one cup of regular caffeinated coffee.